Methods and devices for determining a quantity describing the brake circuit pressure are known in various versions from the related art.
German Patent Application No. 43 40 921 describes a brake pressure control system where the brake circuit pressure is estimated for each brake circuit. The hydraulic system disclosed in German Patent Application No. 43 40 921 has two brake circuits. Each of the two brake circuits has two wheels, each connected to the brake circuit by an intake valve and a discharge valve. Each brake circuit also has a precharge pump, a return pump, a return valve and a reversing valve. With the two pumps, a brake pressure can be generated upstream from the intake valves if a brake pressure is to be built up at the wheels. The return valve and the reversing valve are to be driven accordingly. The desired brake pressure can be achieved in the respective brake wheel with the intake and discharge valves assigned to the respective wheel. Based on one brake circuit, valve control signals are determined at least for the intake valves from setpoint brake pressures for the wheel brake cylinders. The brake cylinder pressures enter into the determination of the setpoint brake pressures, with the prevailing brake circuit pressure and the control times of the intake valves being taken into account in the determination of the brake cylinder pressures. The brake circuit pressure is estimated with the help of a recursive method. Distinction is made between two situations in estimating the brake circuit pressure. In one situation, the required pressure buildup is available, i.e., both the precharge pump and the return pump are receiving current, and the return valve and the reversing valve are connected accordingly. It is assumed that in this situation the two pumps are supplying a constant volume flow. The new value for the estimated brake circuit pressure is obtained as a function of the old estimated value for the brake circuit pressure, the control times of the intake valves in the brake circuit, the wheel brake cylinder pressures and the admission pressure set by the driver. In the other situation, both pumps are turned off. The new value for the estimated brake circuit pressure is obtained here as a function of the old estimated value for the brake circuit pressure and the admission pressure set by the driver. The old estimated value for the brake circuit pressure is weighted with a constant factor so that the resulting reduction in pressure in the brake circuit is simulated.
The method according to the present invention and the device for determining the quantity representing the brake circuit pressure according to the present invention can be used in combination with systems for controlling brake slip or drive slip and in combination with systems for controlling a quantity describing the driving dynamics of a vehicle. Systems for regulating drive slip or brake slip are described in a general form, for example, in the book "Bremsanlagen fur Kraftfahrzeuge" (Brake System for Motor Vehicles) published by Robert Bosch GmbH of Stuttgart, VDI Verlag, Dusseldorf, 1.sup.st edition, 1994. Systems for controlling a quantity describing the driving dynamics of a vehicle are described, for example, in the article "FDR-Die Fahrdynamikregelung von Bosch" (Bosch Method of Regulating driving Dynamics) published in Automobiltechnische Zeitschrift (ATZ), (Automotive Engineering Journal) vol. 96, no. 11 (1994) pp. 674-689.
The object of the present invention is to improve the determination of a quantity describing the brake circuit pressure.